1. Technical Field
The present invention relates to a power line communication apparatus, a power line communication system, and a registration processing method.
2. Background Art
A power line communication apparatus that performs power line communication (PLC: Power Line Communication) by use of a power line can establish power line communication with another power line communication apparatus.
FIG. 15 shows an example communication environment of a power line communication apparatus. In the communication environment shown in FIG. 15, a plurality of L1-phase circuit breakers and L2-phase circuit breakers are provided in order to supply L1-phase electric power and L2-phase electric power to household electric appliances (consumer electronics) and power line communication apparatuses. Power lines are connected to the respective L1-phase and L2-phase circuit breakers. Household electric appliances and power line communication apparatuses are connected to the respective power lines by way of; for instance, outlets provided on walls. For instance, a power line communication apparatus 1500A is connected to a power line 700A by way of an outlet 1510A. A power line communication apparatus 1500B is connected to a power line 700B by way of an outlet 1510B. A power line communication apparatus 1500C is connected to a power line 700C by way of an outlet 1510C. Further, there are cases where electric equipment, such as power line communication apparatus and a household electric appliance, is connected to the outlet by way of a power strip.
As mentioned above, in a communication environment for power line communication, a variety of pieces of electric equipment, such as an electric device that does not perform power line communication, an electric device that implements power line communication, an electric device that causes a lot of noises, an electric device having a low impedance, and an electric device that does not affect another device in relation to power line communication, are connected to various power lines.
In a background power line communication, a communication characteristic is often deteriorated under various circumstances provided below.
As an example of deterioration of a communication characteristic, there may be an occurrence of attenuation of a signal due to a long distance between power line communication apparatuses that perform power line communication (e.g., the power line communication apparatus 1500A and the power line communication apparatus 1500C).
When power line communication is established between a power line communication apparatus connected to the L1-phase power line and a power line communication apparatus connected to the L2-phase power line (e.g., between the power line communication apparatus 1500A and the power line communication apparatus 1500C or between the power line communication apparatus 1500B and the power line communication apparatus 1500C), a signal sometimes undergoes attenuation for reasons of a phase difference.
Moreover, a communication characteristic achieved between power line communication apparatuses (e.g., between the power line communication apparatus 1500A and the power line communication apparatus 1500B or between the power line communication apparatus 1500A and the power line communication apparatus 1500C) is sometimes deteriorated under the influence of noise caused by a household electric appliance (e.g., a household electric appliance 1520A) connected to the power line.
Further, when a power line communication signal is absorbed by a household electric appliance having low impedance (e.g., a household electric appliance 1520B), signal attenuation often arises in power line communication between power line communication apparatuses (e.g., between the power line communication apparatus 1500A and the power line communication apparatus 1500B or between the power line communication apparatus 1500B and the power line communication apparatus 1500C).
A communicable distance over which the power line communication apparatuses can implement power line communication often becomes shorter as a result of occurrence of such deterioration of the communication characteristic.
A transmission device for performing retransmission process when a receiving side cannot have correctly received transmitted packet data has been known as an example technique for preventing deterioration of communication characteristics. The transmission device has parameter control unit that can switch a transmission parameter at the time of transmission of packet data according to a transmission channel state; transmission data control unit that divides stored retransmission data into a plurality of packets and that provides adaptive modulation control unit with the packets when transmission of an amount of data, which is to be performed for the case of new transmission, cannot be assured at the time of performance of retransmission; and adaptive modulation control unit that controls a modulation scheme and a decoding ratio in accordance with a transmission parameter switched by the parameter control unit in relation to each of the plurality of divided packets provided by the transmission data control unit and that sequentially transmits the plurality of packets as retransmission (see; for instance, JP-A-2007-336583).
Incidentally, in order to establish safe, reliable communication among two or more power line communication apparatuses, the power line communication apparatuses perform processing (hereinafter called registration processing) for bringing power line communication apparatuses into a communicable state. Authentication and security setting are performed through registration processing, whereby there is registered information about power line communication apparatuses serving as slave devices whose registration processing is managed by a power line communication apparatuses serving as a master device for managing registration processing.
A related-art registration processing is briefly described by reference to FIG. 16. Processing is based on the assumption that registration processing is performed between a power line communication apparatus 1600A serving as a master device and a power line communication apparatus 1600B serving as a slave device. When the power line communication apparatus 1600B has transmitted a registration request message (step S801), the power line communication apparatus 1600A transmits a receive ACK (a receive response) to the registration request message (step S802). When the receive ACK message responding to the registration request message shows permission, the power line communication apparatus 1600A transmits a registration start message to the power line communication apparatus 1600B (step S803), and the power line communication apparatus 1600B transmits to the power line communication apparatus 1600A a receive ACK responding to the registration start message (step S804). When transmission of the registration start message and transmission of the receive ACK responding to the registration start message are performed, various pieces of information confidential between the power line communication apparatuses (e.g., MAC addresses unique to the power line communication apparatuses, a random number generated from a Time stamp, or the like) is transmitted to each other. The respective power line communication apparatuses 1600A and 1600B generate unique keys from various pieces of mutually-transmitted information. The power line communication apparatus 1600A transmits a successful registration notice message to the power line communication apparatus 1600B (step S805), thereupon completing registration processing. Related-art registration processing, such as that mentioned above, is hereinafter also referred to as basic registration processing.
Since the communicable distance of the power line communication apparatus becomes shorter for reasons of previously-described deterioration of the communication characteristic, the related-art power line communication apparatus often cannot correctly carry out registration processing. In the meantime, when a change is made to the transmission parameter such that the communicable distance becomes longer at the time of transmission of a signal in consideration of deterioration of the communication characteristic, registration processing is successfully carried out in conjunction with; for instance, a power line communication apparatus of a neighboring house, so that desired registration processing cannot be correctly carried out.
The present invention has been conceived to solve the situation and aims at providing a power line communication apparatus, a power line communication system, and a registration processing method that, even when a plurality of power line communication apparatuses are connected to a power line, enable reliable registration processing in conjunction with desired power line communication apparatuses without transmission of a registration signal over a distance up to a point where registration can be performed along with a power line communication apparatus of a neighboring house, by controlling a communicable distance.